This application is based on and incorporates herein by reference Japanese Patent Applications No. 11-366455 filed Dec. 24, 1999 and No. 2000-73965 filed Mar. 13, 2000.
This invention relates to an activating device for a vehicle passenger protection system such as an air-bag system or a belt pretensioner installed in an automotive vehicle.
In an activating device of an air-bag system for use in a car, a mechanical switch has been employed as a switch for passing an activating current through a squib. This mechanical switch has been used in the activating device as a safety switch for operating the squib, because it is less likely to operate erroneously by electrical noise, improper operation of a microcomputer having as its main unit a CPU, or dewing or wetting.
However, the mechanical switch is expensive and large. Also, because the time for which the mechanical switch stays closed is short, it cannot provide the closure holding period needed for delay control used when a delay is to be provided between the operation of a belt pretensioner and the deployment of an air-bag or when a delay is to be provided between a first stage and a second stage of a two-stage deployment air-bag.
Consequently, in recent years, with the object of reducing cost and improving passenger protection performance, there has been an increasing need for the mechanical switch to be replaced with an electronic switching device. However, when replacing the mechanical switch with an electronic switching device, it is necessary to ensure that the electronic switching device will not operate erroneously as a result of electrical noise, improper operation of a microcomputer, or wetting.
It is therefore an object of the present invention to provide an activating device for a vehicle passenger protection system wherein erroneous activating operation caused by improper operation of a microcomputer or electrical noise is prevented even though electronic switches are used to operate a squib.
It is another object of the invention to provide an activating device for a vehicle passenger protection system wherein erroneous operation caused by dewing or wetting is prevented even when electronic switches are used to activate a squib.
According to the present invention, an activating device for a passenger protection device uses a pair of acceleration sensors and a plurality of electronic switching devices. The electronic switching devices are connected in series with a squib to allow an activating current to pass through the squib when turned on. A first circuit is provided to determine whether the vehicle is in a collision on the basis of detection outputs of the acceleration sensors. A second circuit is provided to determine whether the vehicle is in the collision on the basis of the detection output of one of the acceleration sensors. An ON-prohibiting circuit is provided to prohibit one of the electronic switching devices from being switched on when it is determined by one of the first and the second circuits that the vehicle is not in the collision. The ON-prohibiting circuit suspends this prohibition when it is determined by the one of the first and the second circuits that the vehicle is in the collision. The first circuit is a microcomputer provided as a hardware unit separately from the second circuit.